Adds Semantic Label to Sign-Up Checkbox

[martinmckenna]

Purpose

adds semantic <label /> element to sign up form terms and conditions checkbox, so it's more accessible to scree readers and also enables the ability to click the label to check/uncheck the box

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Thanks for making this project! i wanted to poke around and see how it worked exactly, which is why i created this PR. i will say this has a few pain points for developing locally

[martinmckenna]

is this ever gonna get merged? I can close if not but this is a no-brainer PR

[martinmckenna]

lame...okay closing